Method of manufacturing a multiple-electrode discharge tube

ABSTRACT

A multiple-electrode discharge tube comprises a plurality of disc electrodes arranged one above another and fused with the envelope therefor. Each of the odd-numbered electrodes has a reduced diameter and a reduced thickness as compared with the even-numbered electrodes. Fusion takes place by way of high frequency heating coils disposed around the electrodes of reduced thickness. This provides a uniform heating of all of the electrodes for fusion, and avoids partial overheating of the envelope.

United States Patent 91 Furuta Nov. 13, 1973 [54] A 2,899,590 8/1959Sorget a1 313/257 X MULTIPLE ELECTRODE DISCHARGE 2,910,607 10/1959McCullough et a1. 313/257 X 2,279,249 4/1942 Roman 313/250 X TUBEInventor:

Assignee: Kabushiki Kaisha Sankosha,

salelsbjna aw -kw pa Filed: Dec. 27, 1971 Appl. N0.: 211,917

Shigeru Furuta, Tokyo, Japan Foreign Application Priority Data March 9,1971 Japan 46/12185 U.S. Cl 29/2516, 313/249, 313/296, 313/299, 313/300Int. Cl. H0lj 9/18, H01j 21/10, H01j1/88 Field of Search 313/299, 300,301, 313/296, 249, 250, 257, 29/25.16

Primary ExaminerPaul A. Sacher Attorney-E. F.- Wenderoth et a1.

[57] ABSTRACT A multiple-electrode discharge tube comprises a pluralityof disc electrodes arranged one above another and fused with theenvelope therefor. Each of the oddnumbered electrodes has a reduceddiameter and a reduced thickness as compared with the even-numberedelectrodes. Fusion takes place by way of high frequency heating coilsdisposed around the electrodes of reduced thickness. This provides auniform heating of all of the electrodes for fusion, and avoids partialoverheating of the envelope.

[' References Cited 3 Claims, 5 Drawing Figures UNITED STATES PATENTS2,409,855 10/1946 Hillyer et al. 313/300 X PATENTED NOV 1 3 I973 FIG. I

FIG. 2

FIG. 3

FIG. 4

fl I HEATING TIME t INVENTOR Shigeru Furuta mmDkwag 2 IME wum.w smutATTORNEB METHOD OF MANUFACTURING A MULTIPLE-ELECTRODE DISCHARGE TUBE Theinvention relates to a multiple-electrode discharge tube of thelayer-built type, and in particular, to such discharge tube having morethan two electrodes in which an intermediate electrode is adisc'electrode having a diameter greater than either the upper or lowerelectrode. The invention also relates to a method of manufacturing suchdischarge tube.

Prior art multiple-electrode discharge tube of the kind described havebeen fabricated by fusing the electrodes to the envelope of the tubewith high frequency heating, and both top and bottom electrodes as wellas the intermediate electrode were of a common thickness. In those priorart methods, a high frequency coil is disposed around the envelope andis energized to produce magnetic flux which intersects each of theelectrodes to thereby generate heat for fusing purposes. However, inview of the higher flux density around the intermediate electrodecompared to the relatively low density around the upper or lowerelectrode, and because of the greater diameter of the intermediateelectrode, more flux is intersected by the intermediate electrode. As aresult a difference in temperature occurs between this intermediateelectrode and the upper or lower electrode, which results in theenvelope softening initially around the intermediate electrode and thenafter a short time delay around the upper and lower electrodes with atime delay. The delay results in the overheating of the glass envelopeso that it is hotter than is required for fusing with the electrodes.This causes strains to be produced in the glass envelope with consequentpoor quality of the product.

The division of the high frequency coil into two parts disposed tosurround the upper and lower electrodes, respectively, still fails toprevent premature heating and fusing of the intermediate electrode byvirtue of the increased flux density around the intermediate electrodewhich results from the sum of the fields created by the respective coilparts.

Therefore, it is an object of the present invention to provide animproved multiple-electrode discharge tube and a method of manufacturingthe same which overcomes the above difficulty.

For a better'understanding of the invention, it will be described belowwith reference to the drawings in which FIG. 1 is a schematicelevational section of a prior art triode discharge tube of thelayer-built type arranged with a high frequency heating coil,

FIG. 2 is a similar view of the discharge tube constructed according tothe invention,

FIG. 3 is an elevation, partly in section, of the discharge tube shownin FIG. 2,

FIG. 4 shows graphically the relation between the fusing temperature andheating time for various electrode thicknesses and FIG. 5 is anelevational section of the discharge tube constructed according to theinvention, using disc electrodes to constitute a pentode structure.

Referring to the drawings, FIG. 1 shows a prior art discharge tube whichincludes an upper electrode 1, a lower electrode 2 and an intermediateelectrode 4, all of which have an equal thickness. These electrodes arefused with an envelope 3, which may comprise glass, by means of highfrequency heating coil 7. As mentioned previously, more flux isintersected by the intermediate electrode as compared with the upper orlower electrode, with the consequence that the temperatures of theintermediate electrode rises more rapidly than the latter and hence issupplied with an additional amount of heat until the time when the otherelectrodes become sufficiently heated to permit their being fused withthe envelope 3. Such overheating of the intermediate electrode causesstrains in the glass envelope and degrades the quality of the product.

- Referring to FIGS. 2 and 3 which show one embodiment of the invention,the intermediate electrode indicated at 4A has an increased thickness aswill be noted from a comparison with the electrodes 1 and 2. Theintermediate electrode 4A has a discharge electrode 5 and an aperture 6formed therein which provides an ion path for inducing a dischargeacross the electrodes 1 and 2 from the initially occurring dischargeacross the electrode 4A and the electrodes 1 and 2. In FIG. 2, referencenumerals 8 and 9 represent divided parts of a high frequency heatingcoil disposed only around the thinner electrodes 1 and 2, respectively.The assembly is enclosed in a bell jar 10.

Referring to FIG. 4 which shows the relation between the fusingtemperature and the heating time, curve designated A represents thediagram for the thin electrodes l and 2, curve B for a thin intermediateelectrode 4, and curve C for a thick intermediate electrode 4A. Thepoints at which fusing takes place are indicated at 17 and 18 on therespective curves.

FIG. 5 illustrates another embodiment of the invention and shows adischarge tube having five electrodes.

The top electrode 1 is thin, the second electrode 11 from the top isthick, the third electrode 12 is thin, the fourth electrode 13 is thick,and the bottom electrode 2 is thin. In other words, odd-numberedelectrodes are thin and smaller in diameter than even-numberedelectrodes, while even-numbered electrodes are thick and greater indiameter. High frequency heating coils 14, 15 and 16 are disposed onlyaround thin electrodes 1, 12 and 2.

From the foregoing description, it will be appreciated that the problemassociated with the manufacturing of a discharge tube as illustrated inFIG. 1 is solved in accordance with the invention by replacing theordinary intermediate electrode 4 by a thicker one as shown at 4A inFIG. 2. While more flux from the high frequency heating coil isintersected by the thick intermediate electrode 4A than by the upper orlower electrode 1 or 2, the increased heat capacity of this intermediateelectrode due to its increased thickness causes a shift in the time forreaching the fusing temperature to the point 18 of FIG. 4. By contrast,where all of the electrodes are of a common thickness as illustrated inFIG. 1, the intermediate electrode will reach the fusing temperature atthe point 17 (curve B) of FIG. 4, while the upper and lower electrodesreach the same temperature at the point 18 (curve A) of FIG. 4, therebyproducing a time delay t. The invention eliminates this delay, andpermits the intermediate electrode 4A to be sealingly fused concurrentlywith the upper and lower electrodes, thereby achieving the favorableresult of an improved product.

It has been found that when the thick intermediate electrode 4A is used,dividing the high frequency heating coil into two parts disposed onlyaround the upper and lower electrodes 1 and 2 also avoids the time delayand permits concurrent fusing of all of the electrodes, even though theflux density may be increased around the intermediate electrode ascompared with the other electrodes. lt has also been found that suchdivision of the high frequency heating coil is effective for amultiple-electrode discharge tube where there is an intermediateelectrode of similar diameter and thickness as the top and bottomelectrodes, as illustrated at 12 in FIG. 5.

While the envelope of the discharge tube has been described ascomprising glass, it should be obvious that it may comprise ceramicmaterial. Where a ceramic envelope is employed, the electrode isprovided with a melting metal for fusion with the envelope. For thisarrangement, the invention is again effective to prevent undesired flowand attachment of the melting metal to other functional surfaces whichmight occur if the electrodes involve differential time periods to reacha melting temperature, and which would degrade their mechanical strengthand other functions. Thus, there has been described an extremely simpleand effective means for manufacturing, with good yield, amultipleelectrode discharge tube of the layer-built type in which anintermediate disc electrode positioned between upper and lower discelectrodes has a greater diameter than the latter.

Having described the invention, what is claimed is 1. A method ofmanufacturing a multiple-electrode discharge tube of the layer builttype comprising the steps of providing a first electrode member of areduced thickness and a reduced diameter and providing a secondelectrode member having a thickness and diameter greater than thethickness and diameter of said first electrode member, disposing saidfirst and second electrode members one above another in alternatingfashion and interposing portions of a cylindrical glass envelopetherebetween, extending the outer end of the respective electrodemembers directly through and externally of the envelope, placing a highfrequency heating coil around the outer periphery of the envelope so asto oppose only the first electrode member and such that the end of themagnetic flux from the coil is intersected by the second electrodemember, and energizing the coil to heat and fuse the first and secondelectrode members with the envelope.

2. The method as claimed in claim 1 further comprising providing aplurality of first electrode members, placing a corresponding pluralityof high frequency heating coils around the outer periphery of theenvelope so as to oppose the corresponding first electrode members andenergizing said coils to heat and fuse said plurality of first electrodemembers and said second electrode members with said envelope.

3. The method as claimed in claim 2 further comprising providing aplurality of second electrode members and alternating said firstelectrode members with said second electrode members.

1. A method of manufacturing a multiple-electrode discharge tube of thelayer built type comprising the steps of providing a first electrodemember of a reduced thickness and a reduced diameter and providing asecond electrode member having a thickness and diameter greater than thethickness and diameter of said first electrode member, disposing saidfirst and second electrode members one above another in alternatingfashion and interposing portions of a cylindrical glass envelopetherebetween, extending the outer end of the respective electrodemembers directly through and externally of the envelope, placing a highfrequency heating coil around the outer periphery of the envelope so asto oppose only the first electrode member and such that the end of themagnetic flux from the coil is intersected by the second electrodemember, and energizing the coil to heat and fuse the first and secondelectrode members with the envelope.
 2. The method as claimed in claim 1further comprising providing a plurality of first electrode members,placing a corresponding plurality of high frequency heating coils aroundthe outer periphery of the envelope so as to oppose the correspondingfirst electrode members and energizing said coils to heat and fuse saidplurality of first electrode members and said second electrode memberswith said envelope.
 3. The method as claimed in claim 2 furthercomprising providing a plurality of second electrode members andalternating said first electrode members with said second electrodemembers.